A recording material comprising an electron-providing colorless dye and an electron-accepting compound is known for use as pressure-sensitive paper, heat-sensitive paper, photosensitive pressure-sensitive paper, electric heat-sensitive recording paper, heat-sensitive transfer paper, etc. These recording materials are further described in British Patent 2,140,449, U.S. Pat. Nos. 4,480,052, and 4,436,920, JP-B-60-23992 (The term "JP-B" as used herein means an "examined Japanese patent publication"), and JP-A-57-179836, JP-A-60-123556, and JP-A-60-123557 (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
In the field of recording materials, extensive study has recently been made to improve their properties such as (1) color density and sensitivity and (2) storage stability of nonimage and image portions.
Electron-accepting compounds to be used in combination with electron-providing colorless dyes include various compounds such as bisphenol A, p-hydroxybenzoic ester and bis-(4-hydroxyphenyl)sulfone. However, all these compounds have disadvantage in color density, color sensitivity or storage stability (e.g., weathering resistance, chemical resistance, plasticizer resistance). For example, bis-(3-phenyl-4-hydroxyphenyl)sulfone, when incorporated into a heat-sensitive recording material, is poor in preservability of the nonimage portion as demonstrated by fog on the background with marking ink, fluorescent ink, etc. Further, 4-isopropoxy-4'-hydroxydiphenylsulfone, when incorporated into a heat-sensitive recording paper, exhibits a high color density and sensitivity, but leaves much to be desired in chemical resistance as demonstrated by coloring on the background with marking ink, fluorescent ink, etc. and fading of typed images.
The inventors have found that specific compounds are useful for the improvement of these properties.